Fluoroelastomers are heat stable and resistant to a wide range of chemical reagents. For this reason fluoroelastomers are typically used for making O-rings, gaskets, oil seals, diaphragms, hoses, tubings, rolls and sheeting materials, in particular in the automotive industry and chemical industry.
Fluoroelastomers are typically obtained by curing (cross-linking) a generally amorphous fluoropolymer. To achieve sufficient cross-linking the amorphous fluoropolymers contain cure sites, which are reactive groups that can undergo cross-linking reactions in the presence of suitable cross-linking agents.
A commonly used cure system is based on a peroxide cure reaction using appropriate curing compounds having or creating peroxides, which in turn are believed to generate free radicals. The fluoroelastomers suitable for use in peroxide curing systems (peroxide curable fluoroelastomers) contain reactive sites which include halogens, such as bromine and/or iodine. It is generally believed that the bromine or iodine atoms are abstracted in the free radical peroxide cure reaction, thereby causing the fluoropolymer molecules to cross-link and to form a three dimensional network.
For example, the reactive cure sites may be introduced by copolymerizing comonomers containing cure sites or by using chain transfer agents containing cure sites. An example for this approach is described in U.S. Pat. No. 5,717,036. Such methods, however, require the use of organic solvents in case of solvent based polymerisations. The use of solvents, however, is disadvantageous. Solvents have to be removed and recycled which increases the costs of the polymerisation. Alternatively, the polymerisation can be carried out in aqueous phase by aqueous emulsion polymerisation. These methods are known to require the use of emulsifiers or fluorinated additives. The emulsifiers are desirably removed from the product which leads to increased process steps and costs also.